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Difficulty: MediumDNS Lookup and Name Resolution Roles in Enterprise Networks

A network administrator configures the IP address of an external DNS server on a Cisco IOS router using the command `ip name-server 10.1.1.1`. However, when attempting to ping a remote server by its hostname (`ping server1.example.com`), the router immediately fails to resolve the name and no DNS query packets are transmitted. Which command must be entered in global configuration mode to enable the router to perform DNS queries for hostname resolution?

  1. ip domain lookupAnswer
  2. B
    ip dns server
  3. C
    ip domain name example.com
  4. D
    ip helper-address 10.1.1.1

Answer

The command `ip domain lookup` must be configured in global configuration mode to enable Cisco IOS DNS hostname resolution.
The `ip domain lookup` command globally enables the DNS host name resolution feature on a Cisco IOS router. Without this command enabled, the router will not generate DNS request packets to configured DNS servers specified by `ip name-server`.

Step-by-Step Solution

1
Identify the role of the Cisco IOS device in name resolution
The router is acting as a DNS client trying to resolve hostnames to IP addresses for local CLI operations.
Configuring `ip name-server` defines the destination DNS server IP address, but the DNS lookup process must be globally enabled on the device.
2
Determine the global command required to enable client DNS lookups
Executing `ip domain lookup` enables the IP DNS client feature in Cisco IOS.
If DNS lookup is disabled (via `no ip domain lookup`), Cisco IOS will not initiate DNS queries over UDP port 53 even if valid name servers are defined.

Key Concept

Cisco IOS DNS Client Configuration and Hostname Resolution Mechanics
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Topics

DNS Lookup and Name Resolution Roles in Enterprise Networks

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